Neither Velasquez nor Diccionario de la Lengua Española (Real Academia Española) have the word 'ondiña' (with the tilde).
Ondina is defined as a mythological being, a nymph (Diccionario), or water sprite (Velasquez).

Galician usage may be beyond the ability of the persons involved in the website that I took the song from.
Are there any other mis-usages in the translation quoted above? I have lost the website.